Power grid topology identification is not only an important part of the advanced application software of the power network management system, but also the basis for a variety of analytical calculations. The paper proposes a new method to speed up the power grid topology identification, which solves the disadvantages of the matrix large computation and slow computation speed. The method uses the node-branch incidence matrix to represent the basic topological structure of the network, defines the matrix "or" or "and" operation and switch state vector, employs the symmetric elimination to reduce the order number of the adjacency matrix and applies the apply symmetry to the process of finding the connected matrix, thereby realizing the network dynamic topology. Compared with the traditional algorithm, the algorithm can reduce amount of calculation and accelerate the computation speed, which is suitable for topology identification of complex power grid. This work is supported by Science and Technology Project of State Grid Henan Electric Power Company (No. 52171015023Z).